The present application is directed to an apparatus with a receiving zone for receiving solid material; a transferring zone for transferring said solid material; and, optionally, a releasing zone for releasing the solid material, e.g. to a further moving surface, and with a moving endless surface moving in and through said zones, which has a multitude of primary cavities and secondary cavities receiving the solid material. The primary cavities are connected to a vacuum system in the transferring zone, and the secondary cavities are not connected to a vacuum system in said transferring zone. Thus, only the primary cavities transfer the solid material e.g. to the further moving surface. Thereby, both primary and secondary cavities typically are connectable/connected to a vacuum system in the receiving zone. The present application also relates to a method for receiving and transferring and releasing solid material, by use of the apparatus herein, or as described herein.
In the last decades, various processes have been proposed for making absorbent cores with fibers and/or superabsorbent polymer particles (SAP particles), also referred to as absorbent gelling polymer particles (AGM particles), including processes whereby said material is laid down on a moving surface, such as a drum surface, with one or more reservoirs and held onto said surface by vacuum. These approaches include indirect printing methods, whereby the AGM and/or fibers are taken up by a drum from one or more bulk storage(s) of said fibers and/or AGM particles, and whereby the drum then rotates towards a substrate such as a nonwoven, to then release the AGM and/or fibers onto the substrate. The drum may have one or more cavities, each being in the shape of a diaper core, that is then filled with fibers and/or AGM. However, such a complete diaper core shapes are difficult to transfer completely and accurately at high speed onto a second surface, such as a moving nonwoven web. In more recent years, it has been proposed to deposit fibers and/or AGM into smaller cavities. Such a multitude of smaller cavities may then together be in the form of a diaper core, so that when the AGM content of all the cavities is transferred onto a second surface, like a nonwoven web, a core is formed. This is for example described in EP-A-1621165. With such methods, a more accurate transfer of the solid material can be achieved, so that the resulting absorbent core may have a specific profile or distribution, such as a predetermined pattern,MD-, CD-, or thickness-profile, corresponding to the pattern/depth of the cavities.
Such proposed indirect printing processes are in some instances difficult to run at high speed, for example at speeds of more than 800 or more than 1000 parts (e.g. absorbent cores) per minute, and/or when fine particulate material is used, and/or when small (and large quantities of) cavities are used. Likewise, in such instances the solid material (such as fibers and/or AGM particles) are not always satisfactorily received by the cavities, resulting in inaccurate filling of the cavities, and hence insufficient transfer of the material and hence inconsistencies in the resulting absorbent cores.
Furthermore, when the process or apparatus is such that vacuum is needed to fill the cavities accurately, it is important that the vacuum/air flow through the cavities and/or solid materials is about constant, and/or that it is important that the vacuum/air flow per surface area is sufficient and about constant. When the process is very fast, and/or when the cavities are very small and/or when the particle material is of fine (particle) size, solid material may build up locally above the cavities, prior to flowing into the cavities, reducing the airflow (vacuum suction) in such areas. This may lead to inaccurate filling and insufficient transfer. For example, when the cavities are in the form of a pattern and thus have areas between the cavities, the vacuum/airflow may not always be sufficient or not sufficiently constant per surface area.
Furthermore, if the moving surface (such as a print roll or drum) comprises substantial zones (extending in machine direction, MD and cross-machine direction, CD) without cavities, for example corresponding to the zones between absorbent cores (of the web of absorbent cores produced by the method or with the apparatus) where for example the cores are to be separated from one another, continuous deposition of the solid material by the apparatus or process may result in build-up of said solid material. Even if a means is present to remove this build-up about immediately, such as a scraper blade, the air flow (vacuum) may already be impeded, and hence inaccurate filling of the cavities may occur.